1. Field of the Invention
The present invention relates to an apparatus for driving a magnetic head mounted on a rotary cylinder of, e.g., a video tape recorder, and more particularly, it relates to a magnetic head driving apparatus employing a monolithic piezoelectric bimorph element.
2. Description of the Prior Art
FIG. 14 shows an example of a conventional magnetic head driving mechanism of a video tape recorder. A magnetic head 2 is fixed to an end of a monolithic bimorph member 1, the other end of which is fixed to and supported by a support member 3. As shown in FIG. 15, the monolithic bimorph member 1 comprises a sintered body wherein a plurality of electrodes 4 to 8 are stacked alternating with a plurality of ceramic layers. The electrodes 4, 6 and 8 are electrically connected with each other by a connecting electrode 11 formed by coating conductive paste on an end surface of the sintered body. The electrodes 5 and 7 are connected respectively to conductive parts 12a and 12b formed on the other end surface of the sintered body, at which end surface the electrodes 5 and 7 are partially exposed. The conductive parts 12a and 12b are electrically connected with each other by a connecting electrode 13, whereby the electrodes 5 and 7 are electrically connected with each other.
The aforementioned monolithic bimorph member 1 is obtained in the following procedure: A sintered body 21 is prepared as shown in FIG. 16 and then the electrode 5 is supplied with a potential of V volts, the electrode 7 is supplied with a potential of -V volts and the electrodes 4, 6 and 8 are supplied with potentials of zero volts as typically shown in FIG. 17, to polarize the ceramic layers interposed between the electrodes 4 to 8 in the directions shown by arrows in FIG. 17. Then the conductive parts 12a and 12b are connected by the connecting electrode 13 as hereinabove described, thereby to obtain the monolithic bimorph member 1.
Since the monolithic bimorph member 1 comprises the sintered body 21, the ceramic layers interposed between the electrodes 4 to 8 can be reduced in thickness, thereby to increase the amount of displacement per applied voltage. Thus, the magnetic head 2 can be displaced by low voltage in the structure as shown in FIG. 14.
In the aforementioned structure, however, it is difficult to fix the magnetic head 2 in a correct attitude. Namely, the electrodes 4, 6 and 8 of the monolithic bimorph member 1 are electrically connected with each other by the connecting electrode 11, which is formed by coating conductive paste on the end surface of the sintered body 21. Thus, the conductive paste must be coated to reliably extend over the upper and lower edges of the end surface of the sintered body 21, in order to securely connect the electrodes 4 and 8 with each other. As a result, the connecting electrode 11 is hardened with its upper portion upwardly extending beyond the upper surface of the sintered body 21, i.e., beyond the electrode 4, as shown in an enlarged manner in FIG. 18. This, it is extremely difficult to fix the magnetic head 2 with its lower surface parallel with the electrode 4, and therefore the magnetic head z is apt to be fixed with an inclined attitude with respect to the body 21, as shown in FIG. 18.
On the other end of the monolithic bimorph member 1, the conductive paste for forming the conductive parts 12a and 12b extends over the lower surface 21a of the sintered body 21 since the sintered body 21 is small in thickness (about 300 .mu.m). Thus, it is extremely difficult to fix the monolithic bimorph member 1 in a correct attitude to the support member 3 as shown in FIG. 19 in an enlarged manner.
The aforementioned problem also takes place in the case where the connecting electrode 11 and the conductive parts 12a and 12b are Ag baked electrodes, since the sintered body 21 is considerably small in thickness.